Higgs boson mass measurement using $H\to ZZ\to 4\ell$ decays at CMS

Abstract: A summary of the methods used to make a precision measurement of the Higgs boson mass is presented. The final mass value for the Higgs boson is measured to be $m_{\rm H} = 125.26 \pm 0.21\ \mathrm{GeV}$. This analysis considers the $\mathrm{H} \rightarrow \mathrm{Z}\mathrm{Z} \rightarrow 4\ell$ channel ($\ell = e, \mu$), using proton-proton collision data collected in 2016 corresponding to an integrated luminosity of $35.9\ \mathrm{fb}^{-1}$ at $\sqrt{s} = 13$ TeV by the CMS experiment at the LHC. A mass constraint is imposed on the invariant mass of the two leptons coming from the mostly on-shell Z boson to refit the lepton momenta and, hence, improve the measurement of the Higgs boson mass, per-event. The mass of the Higgs boson is extracted using a three-dimensional likelihood fit, which uses three observables per-event: (1) the refitted four-lepton invariant mass ($m'{4\ell}$), (2) the refitted four-lepton mass uncertainty (${\mathcal D}'{\rm mass}$), and (3) a matrix element-based kinematic discriminant (${\mathcal D}^{\rm kin}_{\rm bkg}$).